Callister - An introduction - 8th edition

670 • Chapter 16 / Composites
(c) Cite two reasons why there must be a
strong bond between fiber and matrix at
their interface.
16.20 (a) What is the distinction between matrix and
dispersed phases in a composite material?
(b) Contrast the mechanical characteristics
of matrix and dispersed phases for fiberreinforced
composites.
Polymer-Matrix Composites
16.21 (a) Calculate the specific longitudinal
strengths of the glass fiber, carbon fiber, and
aramid fiber–reinforced epoxy composites
in Table 16.5 and compare them with those
of the following alloys: tempered (315C)
440A martensitic stainless steel, normalized
1020 plain-carbon steel, 2024-T3 aluminum
alloy, cold-worked (HO2 temper) C36000
free-cutting brass, rolled AZ31B magnesium
alloy, and annealed Ti-6Al-4V titanium
alloy.
(b) Compare the specific moduli of the same
three fiber-reinforced epoxy composites
with the same metal alloys. Densities (i.e.,
specific gravities), tensile strengths, and
moduli of elasticity for these metal alloys
may be found in Tables B.1, B.4, and B.2, respectively,
in Appendix B.
16.22 (a) List four reasons why glass fibers are
most commonly used for reinforcement.
(b) Why is the surface perfection of glass
fibers so important?
(c) What measures are taken to protect the
surface of glass fibers?
16.23 Cite the distinction between carbon and
graphite.
16.24 (a) Cite several reasons why fiberglassreinforced
composites are used extensively.
(b) Cite several limitations of this type of
composite.
Hybrid Composites
16.25 (a) What is a hybrid composite?
(b) List two important advantages of hybrid
composites over normal fiber composites.
16.26 (a) Write an expression for the modulus of
elasticity for a hybrid composite in which all
fibers of both types are oriented in the same
direction.
(b) Using this expression, compute the longitudinal
modulus of elasticity of a hybrid
composite consisting of aramid and glass
fibers in volume fractions of 0.30 and 0.40,
respectively, within a polyester resin matrix
[E m 2.5 GPa (3.6 10 5 psi)].
16.27 Derive a generalized expression analogous
to Equation 16.16 for the transverse modulus
of elasticity of an aligned hybrid composite
consisting of two types of continuous
fibers.
Processing of Fiber-Reinforced Composites
16.28 Briefly describe pultrusion, filament winding,
and prepreg production fabrication
processes; cite the advantages and disadvantages
of each.
Laminar Composites
Sandwich Panels
16.29 Briefly describe laminar composites. What is
the prime reason for fabricating these materials?
16.30 (a) Briefly describe sandwich panels.
(b) What is the prime reason for fabricating
these structural composites?
(c) What are the functions of the faces and
the core?
Spreadsheet Problems
16.1SS
16.2SS
For an aligned polymer-matrix composite,
develop a spreadsheet that will allow the
user to compute the longitudinal tensile
strength after inputting values for the following
parameters: volume fraction of
fibers, average fiber diameter, average
fiber length, fiber fracture strength, fibermatrix
bond strength, matrix stress at composite
failure, and matrix tensile strength.
Generate a spreadsheet for the design of
a tubular composite shaft (Design Example
16.1)—that is, which of available fiber
materials provide the required stiffness,
and, of these possibilities, which will cost
the least.The fibers are continuous and are